Amplifying system



B. G. POHLMANN AMPLIFYING SYSTEM Filed March 26, 1921 Patented Jan. 20, 1925.

UNITED STAT S PATENT OFFKZE.

BRUNO GERHABD IOHLMANN, F SIEMENSSTADT, NEAR BERLIN, GERMANY, .AS-.

SIGNOR TO SIEMENS 8a HALSKE, AKTIENGESELLSCHAIT, OF S'IEMENSSTADT, NEAR" nnnmn, GERMANY, A oonrommron oroEnMAnY.

nmr'iirrrrno ses me Application Inca item as, 1921, Serial No. 455,820.

i in. Be. it known that I, B H

POHLMANN, a citizen of the German Empire, at Siemensstadt, near Berlin, Gerave invented certain new "and useful" Improvements in Amplifying Systems (for which I have filed applications in Germany, December'fi, 1919; Switzerland, November 4:, 1920; Norway, November 19,'192O';"Holland, November 9, 1920; France, November 9,

1920; Denmark, November 1920; Sweden, November 1, 1920;,England, December '6,

residin 5 many,

19205 y, ecember 4, 1920), of which. the following is a specification; a i l '16 My invention relates to amplifyingcon 11801310118 for telephone lines, and the' like.

In connections'of this kind, with translators interpolated between transmitter, amplifier 20 curethe best efliciency possible, to soselect the impedance of the primary coil"pertain ing. to the pro-translator that itis" equal to that of the transmitter, and the impedance of the primary coils'pertainingto the inter- 2 mediary and end translators so that-it is equal to that of the tube connected into the system, in which case the natural period of the secondary coil (grid winding) is such that it lies within the frequency range of the alternating-currents to be-transmitted, causing itto correspond as far as possible to the" mean frequency thereof, in orderto obtain for the entire frequenc I range the most favourable amplifying e ect 'ossible.

However, a connectionof t e type specified involves the disadvantage ofgrowingmore selective in proportion to the number of translators employed, so' that, for example, when am lifymg speaking currents, 40 any increase of t e amplification will cause speech to become more and more and finally entirely unintelligible.

In the drawings affixed to this specification and forming part thereof, various modifications of electrical connections embodying my invention are illustrated diagrammati cally. In these drawings- I Figures 1 to 3 show the amplifying curves for one or more amplifiers inductively conpled;

Figure 4 shows an amplifying connection embodying a single amplifiertube;

,Figure 4. shows a modification of the dampening means arranged in parallel to the The curve I shows the distortion transformer after the passage of the cur:

distorted secondary of the translator shown in Figure 4; a

F1 ure 5 shows an amplifyingconnection in w ich three amplifier tubes are disposed i in series; and

to i

amplifying tubes coupled by transformers to the line respectively to eachother. -On

quency and the ordinates the am lification of the speaking current represents by milliam res. Y

tion when the selectivity of the transformers the diagram the abscissae represent the fre- I, -The curves of Fig. 1 show the amplifica and receiver, 1t 1s customary, inorder to secorresponds, as usual, to the frequenc 5000.

y the rents through the first transformer, the curve II the distortion after the passage of the second, and the curve III the distortion after the passage of the third transformer. It

is assumed that after each passage through a transformer the-currents are amplified by amplifying tubes.

It is the object of my'invention'to minimizethis distortion and also those resulting from the line itself. This object may be attained in accordance with my invention in connecting capacities in parallel with the secondaries of the transformers chosen so as to distribute the selectivity of the several transformers over the whole range of fire quencies for the purposeof influencing the curve of amplification in such a manner as to.

to diminish the selectivity of the one or the other transformer if'necessary. 1

As may-be readily understood the fre-" quency corresponding to the natural fre-" quency of the secondary coil and transmitted with the least possible loss will be the one that 'will be most damped when connecting an ohmic resistance in parallel to'the trans former. The effect of the ohmic resistance connected in parallel to the secondaries of a transformer thus consists in a proportionate reduction of the 7 maximum of the amplify. mg curve, which again means a reduction of the selectivity and thus of the distortion of the 'speakin .currentsby'; this selectivity.

Thiseffect of t e ohmicresistance connected in parallel to the secondaries of the trans-1' in Fi 2 ohmic resistances are connected in aral elz, to the -lsecondaries of the transormers "for attenuating: the 1 selectivity of the transformers.

with the secondariesoftheztransformers it is however 'not possible to; eliminate the selective character of :the amplifying arrangedue tome'nt and, to eliminate the distortion the line;itself;. 1

formers to" differentappropriated frequencies within theran'ge'ot speaking currents The iefl'ectyobtainable thereby is represented in Fig.- 3.. The curves I, II, III of this figure correspond tothe use of one, two, and] three transformers and amplifying tubes,

the transformershaving each another selec-.

tivity'. Accordingto the curve I the preferred fr uencies are the mean frequencies corresponds to atransformer the. selectivity of which- 'correspon'ds to the. lower, frequencies, sayaabout 3000,;and the curve III currents. ;-through a third transformerthe selectivity I of which corresponds to the higher frequencies say about 7000. The unevenesses in the-curve III may bfiattenm ated for j instance by putting an ohmic resistance in parallel to ,the secondary of the third transformer.

Of course, the distortion of the speaking currents caused by the impedance of the wave. line may alsobe considerablyattenuatedqby-aniappro riatechoice of the select-v tivity of the trans ormers and the damping of the same. This result is obtainable by a suitable combination.ofcapacities and ohmic.

resistances. p v

The different ,degree of selectivity on the partuofthe-translators may be'secure d, in accordancewith my invention, in an. ex 'tremely simple manner. by connecting suitable condensers in parallel to the secondary coils of the translators. The etfecthereby obtained. is disclosed, .for example, by the, curves accordingto, Figs. 1- and 3, of which Fig. 1;. indicates the successive amplifier curves for a three-stage amplification in l which all the translators obtain their natural period it; aaave mge frequency of about e amplifying curves I, II, III H The selectivity of the transformers isin both cases the same, but Y of the trans ators. in theneig borhoodof 5000. The curveII r II shows the amplification obtained when interconnecting a second tube, the fro-trans- .lator possessing a natural perio of 5000 and'the translator intermediate the two tubes ;0ne of,-? 00O.v .The advantage resulting from curve II relatively to curve II according to Fig. 1 will be readily understood. The

lower frequencies show about the same de gree of; amplification as the. mean frequencie's. Again, when employing a third tube, the 't'ranslatorof whichlis tuned to a By ohmic-resistances connected in parallel frequency of about 7000, the curve resulting is that indicated by III.

amplified .toan approximately flike d ree and that therefore distortion is avoide to p a considerable extent. Y

According ,totthe invention this object is I accomplished; bytuning the different trans;-'

From the aforesaid it will be influenced by giving the preference to the higher or lower frequencies, as may be.

.be conveniently removedvby allowing for a suitable de 'ree of selectivity on the part In such cases-where b the natural: periods of t e translators over the entirei frequency range an adequately uniform. frequency curve is nevertheless not corresponds-tothe passage of the speaking;-

obtainable,vitwill be found expedient to combine the suitable distribution of the senatural capacity of the secondary winding is used as a capacity, the number of turns of thiswinding being so dimensioned that any degree of frequency required will be obtained.

, Fig. 4 illustrates an amplifier connection having only a single amplifier tube, in the caseof which, in accordance with my IDVCII',

tion,"-a resistance IV is connected in arallel to the. secondary coil S of the trans ator U,

the said resistance serving to damp the frequencies transmitted. No special damping means are. required to be'inserted for the supplementary translator N, since the primary winding P, is adapted to the resistance ofthe tube R and the secondary winding S to thereceiver '1, so that it will act In the event of the inbut feebly selective. ternal. resistance of the tube becoming so strong that also the natural period of the supplementary translator is located in the selective amplifying range, then it will further be seen that by a suitable selection a of the natural periods of the translators the tone colour may From this will be I ,seen, that the various frequencies have been a. distribution of l prove expedient to connect at this point a suitable resistance in parallel to the secondary coil S, similar to resistance W.

Fig. 5; discloses a series connection of three amplifier tubes R,, R Rg arranged on the same principle. In accordance with my invention, resistances W lV W are connected'in parallel to the secondary windings S S S of the translators U U U i The effect produced by this connection is, with the exception of the dam ing action introduced by the resistances, t e same as in the case of the series connections of this kind already known, so that no further explanation will be required.

In the place of ohmic resistances alone, other damping means, such, for example, as oscillating circuits arranged in parallel to the secondary coils of the translators U, may also be made use of, the inductance L and capacity G of these circuits being disposed in series as indicated in Fig. 4 which may or may not include a resistance W.

Fig. 6 discloses a series connection of three amplifier tubes R R R arranged in accordance with my invention, in which the selectivity of the translators is distributed over the entire frequency range. As shown and similar to the arran ement of Fig. 5, the heating battery B an the anode battery 15, are common to all the tubes.

In accordance with my invention, the capacities G G 0, are connected in parallel to the secondary coils S S S of the translators U U U which capacities are so chosen, for example, that the natural period of circuit S C, has a frequency of 3000, that oas G a frequency of 5000, and that of S G a frequency of 7000. In parallel to coils S S are connected resistances W W in order to damp the selectivity of the systems S C and S C and, at the same time,

secure a uniform degree of amplification.

In the case of the system S C, a resistance of this kind is notprovided in order to secure a more pronounced amplification of the frequency preferred by the selectivity of this transformer. From the aforesaid it will be obvious that by a suitable combination of these means of connection any de sired distortion of the strengthening curve may be secured.

I claim:

1. In an arrangement for amplifying currents of varying frequency in a line for transmitting speech and having a plurality of thermionic amplifiers in cascade connection, means for eliminating the distortions of said currents, comprising transformers for? transmittingcurrents from the line to the amplifier respectively from one amplifier to the other, capacities connected in parallel with the secondaries of said transformers, said capacities being suitably dimensioned so as to render each of the severaltransformers selective to a different frequency within the whole range of-frequencies to correspondingly affect the current in the several stages of amplification to eliminate its distortion over the whole range of frequencies, the selected frequencies being substantiallyuniformly distributed over the desired range.

2. In an arrangement for amplifying currents of varying frequency in a line for transmitting speech and having a plurality of thermionic amplifiers in cascade connection,means for eliminating the distortions of said currents, comprising transformers for transmitting currents from the line to the amplifier respectively from one amplifier to the other, capacities connected in parallel with the secondaries of said transformers, said capacities being suitably dimensioned so as to render each of the several transformers selective to a different frequency within the whole range of frequencies, and ohmic resistances for attenuating the selectivity of one or more of said transformers in order to obtain a uniformly amplified current, the selected frequencies being substantially uniformly distributed over the desired range.

3. In an arrangement for amplifying currents of varying frequency in a line for transmitting speech, and having a plurality of thermionic amplifiers in cascade connection, means for eliminating the distortions of said currents comprising transformers for transmitting the currents from the line to the amplifier respectively from one amplifier to the other, a shunt connection to the secondary of each of said transformers, including a resistance, a self-induction and a capacity, the said three elements being suitably dimensioned so as to render each of the several transformers selective to a different frequency within the whole range of frequencies, to correspondingly afiect the current in the several stages of amplification to eliminate its distortion over the whole range of frequencies, the selected frequencies being substantially uniformly distributed over the desired range.

4. Method of amplifying currents with in a range of varying frequencies through a plurality of stages including amplifiers and transformers disposed therebetween, consisting in rendering the transformers between the stages each selective to a definite different frequency within the total range, the selected frequencies being substantially uniformly distributed over the entire range.

In testimony whereof I aifix my signature.

BRUNO GERHAR-D POHLMANN. 

